There were approximately 53,000 more millionaire households in the U.S. last year than in 2012, according to Phoenix, a market research firm based in Rhinebeck, N.Y. About 6.15 million millionaire households are spread across the U.S., according to the report. That means 1 in every 20 households in the U.S. has more than $1 million in investable assets. Those figures don’t include the value of real estate.

Large movements for many states made the latest millionaire rankings unusual. Maine climbed 11 spots over a single year to No. 25 in 2013. Louisiana jumped 10 to No. 32. Meanwhile, Nevada fell 20 spots to No. 39. Arizona, Florida, Idaho and Michigan all fell by more than 10 positions. From 2011 to 2012, no state changed its rank by more than two positions.

The big swings may suggest economic recovery may have become more uneven last year, said David Thompson, a managing director at Phoenix. “Maine and Louisiana are two states that have seen big turnarounds in their economies,” he said. “In Nevada, the data suggests the state is still feeling the effects of the downturn.”

But no state had a bigger surge than North Dakota. In 2012, North Dakota ranked 43rd, one spot behind Alabama. Last year, it moved up to 29th, one ahead of Florida. North Dakota’s energy boom, especially in the Bakken shale region, is driving the state’s wealth gains. But its people in the oil patch aren’t about to flaunt it.

“The only way you know a Bakken millionaire is he’ll be driving a new truck and might have taken his wife on vacation,” said Kelvin Hullet, president of the chamber of commerce in Bismarck, the state capital.

Mr. Hullet said the energy, health care and technology sectors are all growing in the state — pushing up paychecks of both the working class and affluent. The state’s unemployment rate was 2.6% in November, according to the Labor Department. That was the lowest in the nation by a percentage point.

The result has been a rapid expansion of retailers, restaurants and housing, Mr. Hullet said. But Bismarck hasn’t turned into West Egg. “I’ve seen the occasional Bentley,” he said. “But mostly, North Dakota is the type of place where someone can be very wealthy and you’d never know it.”

The top of the overall rankings didn’t change much. Maryland was No. 1 for the third consecutive year, with 7.7% of households holding more than $1 million in assets. New Jersey, Connecticut and Hawaii followed. Those four states, in various orders, have led the rankings every year since 2006.

Phoenix uses the data to inform clients, which include wealth-management firms.

Related: David Thompson of Phoenix Marketing International joins the News Hub.

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